One recent post indicated a partner received a PR
but that was because of them having a child together and more than a two year relationship.
I think there has been at least one other applicant who has posted about getting PR
because of a long term relationship.
It has not been a common occurrence as a lot of applicants are looking to see how they can usually just get TR with a borderline 12 months.
I think it is something of a slight on COs generally about them having a bad day or not taking to your looks but approach an interview with a bad attitude and it could make all the difference, a bit like dealing with any bureacracy officials.
There is never a guarantee on any visa application and that goes for getting it in a particular format but if your application was sound I would think asking about PR
in an enquiring light polite way rather than in it is my right type of tone would be the best approach.